Process and apparatus for controlling the expansion of puffable materials

ABSTRACT

A process and apparatus for forming a puffed product from particles of a puffable material. The volumetric expansion and the bulk density of the particles is controlled or limited, by applying a fluid medium onto the particles at, or proximate, the discharge opening where the particles are discharged from a high pressure producing apparatus.

llnited States Patent Strommer et a1.

[54] PROCESS AND APPARATUS FOR CONTROLLING THE EXPANSION 0F PUFFABLE MATERIALS [72] Inventors: Palmer K. Strommer; Kenneth J. Valentas; Herbert Neal Dunning, all of Minneapolis, Minn. [73] Assignee: General Mills, lnc.. 22 Filed: June-2, 1969 [211 App]. NO.: 829,550

[52] US. Cl ..99/8l, 99/238, 239/434 [51] Int. Cl. ...A23l l/lS [58] Field of Search ..99/87, 82, 137, 138, 238;

[56] 3 References Cited UNITED STATES PATENTS 1,227,002 5/1917 Rhoades ..99/238R [151 3,666,966 I451 Apr. 18,1972

3,231,387 1/1966 Tsuchiya et-al ..99/82 93,105 7/1869 McCarthy .239/434 X 3,081,948 3/ 1963 Weiss ..239/369 FOREIGN PATENTS OR APPLICATIONS 827,889 1/1952 Germany ..239/434 Primary Examiner-Raymond N. Jones Attorney-L. Me Roy Lillehaugen, Anthony A. Juettner and William C. Babcock [57] ABSTRACT 18 Claims, 5 Drawing Figures PROCESS AND APPARATUS FOR CONTROLLING THE EXPANSION F PUFFABLE MATERIALS The present invention relates to a process and apparatus for expanding a puffable material, and more particularly to a process and apparatus for controlling the volume expansion of a puffable material when it is subjected to a pufiing operation.

Various pufi'ing devices and techniques have been devised for pufiing or expanding a variety of materials such as whole cereal grains, preformed cereal dough bodies or pellets, and the like. According to the known prior art, continuous and/or batch puffing guns and techniques have been used to cause a puflable material to expand or increase in volume by a substantial amount, e.g., up to ten times its original volume. Perhaps ready-to-eat puffed breakfast cereals are the most com-' mon type of product known in this category. As known, kernels such as wheat or rice, or preformed cereal dough pellets,

can be explosively expanded by a substantial amount by subjecting the particle or piece to a puffing operation in a puffing gun; the amount of expansion being determined by the severity of the gun conditions, such as steam pressure and temperature, gun barrel temperature, feed rate of the material into the gun, moisture content of the material, and the like.

While maximum volume expansion of the pufiable material is preferred in many instances, it has been found that lesser amounts of product expansion are ofttimes desired for certain types of products; in such instances, however, partial or complete gelatinization of the starch is still one of the main objectives, as well as a desired product density. According to the known prior art, it is difficult to achieve a limited or controlled product expansion by using known pufling guns and puffing procedures, because in the manufacture of such products, it is important to maximize the degree of starch damage or gelatinization, without severely toasting or puffing the material. In other words, it is difficult to utilize relatively high steam pressure and temperature so as to maximize starch damage, within a relatively short residence time so as to limit the degree of toasting, while still maintaining a desired product density, and a relatively low product expansion.

Accordingly, one object of the present invention is to provide an improved apparatus for puffing particles of puffable material.

Another object is to provide a puffing apparatus havingimproved means for controlling the volume expansion of a puffahis material when subjected to a puffing operation.

A further object is toprovidean improved discharge nozzle for use with a high pressure producing apparatus.

A still further object is to provide a novel process for expanding a puffable material.

Another object is to provide a process for making a pufied product which is at least partially gelatinized during the puffing operation, but which does not exceed a predetermined volume expansion.

Another object is to provide a process for puffing particles of material wherein the volume expansion and the bulk density of the product can be controlled so that they do not exceed predetermined magnitudes.

Other objects and advantages will become apparent from a consideration of the following specification and accompanying drawings. Before proceeding with a detailed description of the invention, a brief description of it will be presented.

Briefly, the invention involves a pufiing apparatus for expanding or puffing particles of a puffable material in such a manner that the starch within the particles is at least partially, and preferably completely gelatinized, but without expanding or increasing the volume of the material beyond a predetermined magnitude. The discharge end of the apparatus includes a nozzle having means for introducing a fluid medium onto the particles of material as they are discharged from the apparatus through the nozzle. The invention also concerns the process for making an expanded or pufi'ed product in an apparatus such as a puffing gun wherein the volume expansion of the product is controlled by introducing or directing a fluid medium onto the particles of material as they are discharged through a discharge nozzle in the apparatus. Application of the fluid medium onto the puffed particles controls or limits the amount of volume expansion so that the resulting product, though partially or completely gelatinized, does not expand in volume beyond a predetermined magnitude. The bulk density of the resulting pufled product can be controlled so as to range within a prescribed minimum and maximum amount, by varying the specific operating conditions.

The invention will best be understood by reference to the following drawings wherein;

FIG. 1 is a partial side elevational view illustrating the invention as fonning a part of the discharge end of a continuous puffing g FIG. 2 is an enlarged partial view showing the invention in greater detail;

FIG. 3 is a partial sectional view illustrating another embodiment of the invention;

FIG. 4 is a partial sectional view illustrating another embodiment of the invention; and

' FIG; 5 is a partial sectional view illustrating still another embodiment of the invention.

While in its broad sense, the presentinvention can be used with various types of pressurized devices from which cooked or gelatinized products are discharged, it has been used with excellent results in conjunction with continuous puffing guns similar to that illustrated and described in US. Pat. No. 3,231,387. Since the gun itself does not form part of the present invention, it will not be illustrated or described in detail, other than to refer to it as one type of pressurized apparatus from which cooked material is discharged, and which can be used in practicing the present invention.

It has been found that the present invention can be used to form an excellent quick-cooking rice product, by subjecting rice kernels to a puffing operation in accordance with the principles of this invention. In the manufacture of products such as quick-cooking rice, it is important to maximize the degree of starch damage without severely toasting or puffing the grain, while at the same time maintaining a product density which will ensure good texture in the cooked product. During the pufiing operation as presently described, the kernels are expanded in size to about 2-4 times their original size. The expanded kernels are substantially gelatinized, they have a product density which falls within a desired range, and when thereafter combined with the'prescribed amount of water and heated for a few minutes, they are transformed into a product which compares most favorably with rice which is cooked in a conventional manner, i.e., by boiling rice kernels for an extended period of time such as 30 minutes. While the invention will be described primarily with rice as the base puffable material other starch containing materials can be used as well, such as corn, wheat, dough pellets, and the like. Some of the examples described below illustrate a number of puffable materials other than rice which have been puffed with excellent results. It might be pointed out that it might be desirable to direct a fluid medium onto particles of material containing little or no starch, as well, as such particles are discharged from an environment of relatively high temperature and pres sure conditions.

Reference is now made to the drawings. FIG. 1 illustrates a puffing apparatus similar to that illustrated and described in US. Pat. No. 3,231,387. Briefly, the structure includes a rotatable cylindrical puffing gun barrel 10 having an inlet end 12 and a discharge end 14. Material to be pufied is introduced into the inlet end 12 through a rotary valve 16. A casing 18 encloses the major portion of the gun barrel l0, and appropriate burners etc., are positioned within the casing for heating the gun barrel. The discharge end 14 of the gun is provided with a flange 20. A rotary union 22 is attached to the projecting end of the barrel, and it is separated from a nozzle 24 by an adapter or cowling 26. The projecting end of the nozzle 24 is attached to -a conduit 28 which operatively connects the discharge end of the gun barrel to a receiver or separator 30,

at which point the puffed particles are separated from the processing fluid medium, such as steam.

FIG. 2 illustrates the discharge end 14 of the gun barrel, and more particularly, the discharge'nozzle 24 and the manner in which it is attached to the gun barrel 10, in greater detail. As depicted, a cone-shaped member 32, which is provided with a flanged end portion 34 and an opening 35 at its apex end, is attached to the flange 20 so that the apex projects into an opening 36 in a plate member 38. The plate 38 is attached to the end of the barrel and separated therefrom by a spacer or sleeve 40. As illustrated, appropriate fastening devices, such as bolts, are provided for maintaining the cone 32, plate 38, spacer 40, and gun barrel in assembled relationship. Thus, as the gun barrel rotates, the cone, spacer, and plate rotate as well.

The rotary union 22 is provided for permitting the nozzle 24 to remain stationary while the gun barrel 10 rotates, while still retaining a pressure-tight seal between the fixed and movable members. Commercially available rotary unions are available which can be used with good results; the Barco Division of Aeroquip Corporation of Barrington, Illinois, for example, manufactures rotary joints similar to item 22 depicted in FIG. 2. Since rotary unions of this type are commercially available items, they will not be described in detail. For purposes of illustration, the rotary union 22 includes a first cylindrical member 42 and a second cylindrical member 44 positioned within the first member in such a manner that it projects through an opening 46 in the end of the member 42. A bearing 48 and a carbon seal 50 are positioned between the surfaces of the two members; the latter acting to prevent pressurized steam from escaping through the opening 46. The union 22 is attached to the discharge end of the gun 14 by means of a ring member 52 which engages a retaining ring 54 positioned in a groove in the outer surface of the member 42; appropriate bolts and spacers are provided for securing the ring member 52 to the plate 38. A sealing member 56 is interposed between the end of the member 42 and the front surface of the plate, for preventing steam from escaping from the apparatus.

The nozzle 24 has a generally cylindrical outer configuration and it is provided with a passage therethrough formed of three parts or portions; a first cylindrical portion or orifice designated by numeral 60 which is positioned between a pair of frusto-conical shaped portions 62 and 64, so that a constriction is formed in the noule. As illustrated, the passage 62 converges from the front end 66 of the nozzle toward the passage 60, and the passage 64 diverges from the passage 60 toward the second or rearward end 68 of the nozzle. The dimension of the passage or orifice 60 can vary within certain limits. A pair of passages or inlets 70 are formed within the nozzle wall so that they extend into the diverging portion of the passage, i.e., portion 64. Fittings 72 and conduits 74 are connected to the nozzle, by appropriate threading, press fitting, or the like, and they are connected to a source of fluid medium (not shown) for introducing the fluid into the nozzle. It might be pointed out that while two passages are shown for introducing the fluid medium into the noule, only a single passage could be provided if desired, or on the other hand, multiple passages could also be provided. Furthermore, if preferred, a manifold could be included which surrounds the noule for providing the fluid medium to a plurality of inlet openings or passages.

The adapter 26 is threadedly connected at one end to the projecting end of the rotary union, and at its other end to the front end 66 of the nozzle 24. In a like manner, the conduit 28 is threadedly connected at one end to the back end 68 of the nozzle; and it is attached to the receiver 30 at its other end by appropriate means.

In operation, particles of a puffable material are fed into the inlet end 12 of the gun and are discharged therefrom through the opening in the cone-shaped member 32. While in the gun barrel, the particles are cooked by subjecting them to a heated pressurized processing fluid such as steam, so that they are at least partially gelatinized, and preferably completely gelatinized. As the particles and the steam are discharged through the opening 35 in the cone, they pass into and through the nozzle 24. As known to those familiar with the gun puffing art, the particles explosively puff or expand in volume as they pass from the high pressure zone in front of the orifice 60, into the nozzle portion 64 and conduit 28, which are under sub stantially zero pressure gauge, or even vacuum, conditions. Application of the fluid medium onto the particles as they pass through the nozzle 24, and more particularly the orifice 60, controls or limits the amount of expansion which takes place. As a result, a puffed product can be obtained which is substantially completely gelatinized, but which has increased in size by only 2-4 times its original volume, and its bulk density is still relatively high, as compared to a puffed ready-to-eat breakfast cereal piece, for example. Under normal operating conditions, the conduit 74 can be connected to an appropriate fluid source requiring little or no pressure, other than that necessary to merely cause the fluid to flow into the nozzle at a desired feed rate. It might be pointed out at this point, that in some instances slurries formed of water and other ingredients might be used as the fluid medium; in such instances, it might be necessary to provide a pump for forcing the slurry into the nozzle.

FIGS. 3 and 4 illustrate similar nozzle arrangements. As shown in FIG. 3, a single inlet 80 is provided in a noale 82, and it is positioned on the pressure side of the orifice 84, i.e., into the converging portion 86 of the nozzle passage. Since the pressure within the first portion of the nozzle is normally quite high, it is necessary to provide a pump 88 for forcing the fluid into the nozzle. In all other aspects, this embodiment works in the same general manner as the apparatus described above.

In FIG. 4, the inlet for introducing a fluid medium into the apparatus is shown as being positioned at 90 in conduit 92, the latter member being connected to the discharge end of a nozzle 94. It has been discovered that the volumetric expansion of a puffable material can be controlled or limited, by placing the fluid injection passage within the conduit, provided that its distance from the nozzle, and more particularly the orifice 96, does not exceed a prescribed distance designated a." Distances as high as 12 inches have been found to work with good results. It should be realized of course, that if the distance is too great, the particles will have expanded by the time the cooling fluid medium is applied to the surface of the particles.

Finally, FIG. 5 illustrates an embodiment wherein a rotary union 100 is attached directly to the discharge end 102 of a gun barrel. As shown, the barrel end has an opening 104 through which the cooked product is discharged. A nozzle 106, similar to that described in FIG. 1, is attached to the projecting end of the rotary union by an adapter 108. As the particles and the steam pass through the opening 104, they pass into the nozzle 106 at which point the particles expand in the same manner described above.

As pointed out above, the apparatus herein described can be used to puff a variety of puffable materials. As disclosed in U.S. Pat. No. 3,231,387, the puffing gun can be operated under a variety of different operating conditions. It has been found that in practicing the present invention, the same general processing conditions as those disclosed in the above patent can be used. Steam is preferably used as the processing fluid, and it is introduced into the gun barrel at a pressure ranging from about 35 to 130 psig and at a temperature ranging from about 285-500 F. It should be recognized of course, that pressures and temperatures outside these ranges might also be used if desired for certain products and under certain operating conditions; the above ranges merely define certain ranges which have been found to work with good results for puffable materials such as rice, corn, and cereal dough pieces. The barrel is maintained at a temperature of about 500-900 F., and it is rotated at a speed of about 28-100 rpm, it is inclined at an angle of about 2564 degrees with respect to a horizontal plane, and its length can vary within quite wide ranges; guns having a length of 10-20 feet and a diameter of 8-10 inches for example, have been used. Nozzle sizes ranging the rotary union, the adapter 26, and through the orifice 60 in from about 76-21/32 inch in diameter have been used with good results. Under normal operating conditions material to be puffed is fed into the inlet end of the gun at a feed rate of about -50 pounds per minute, its moisture content might range from about 5-15 percent, and preferably it is preheated to a temperature ranging from about 100200 F., although this may not be necessary or desired in all instances. Generally, the material is maintained in the gun barrel for about 5-75 seconds, during which time the starch within the material is at least partially gelatinized, and in many instances, complete gelatinization is achieved. In this regard, it might be pointed out that various techniques are known to those in the art for determining the amount of starch damage or starch gelatinization; since these techniques are generally well known, they will not be described in detail.

The fluid medium is introduced into the nozzle 24 at a feed rate which might vary from about 025-50, and preferably about 0.4 to 3.0 pounds per minute. The specific feed rate of the fluid medium will depend upon the particular material being puffed, the desired bulk density of the final product, the amount of volume expansion desired, the feed rate of material into the gun, etc. As noted above, the point of fluid injection into the nozzle can vary, as it can be positioned within the diverging section of the nozzle; it can be positioned on the pressure side of the nozzle; it can be positioned downstream from the nozzle in the conduit attached to the nozzle end; and more than one inlet can be provided for introducing the fluid medium into the nozzle. As pointed out hereinbefore, if the point of injection is on the pressure side of the nozzle, a pump is required having sufficient pressure to force the fluid medium into the nozzle due to the steam pressure within the gun barrel. After the steam and the puffed material have been separated, it may be desirable to cool the product before packaging it or storing it.

Water has been used as the fluid medium with excellent results. The water appears to act as a heat sink, and presumably controls or limits the expansion of, the puffed particles by cooling the particles. Generally it has been found that the water need not be cooled to any specific degree, as room temperature water has been usedwith very satisfactory results. As the water contacts the surface of the particles, it vaporizes and absorbs the heat from the particles, thus controlling the amount of expansion of the particles. Liquid nitrogen has also been used as the fluid medium, with satisfactory results. In addition, it has been found that slurries can be formed and applied onto the particles, by injection into the noule. A slurry formed of water and one or more vitamins for example, can be pumped into the nozzle and applied to the particle surface; this variation serves the additional function of enriching the particles, as well as controlling the amount of expansion. Moreover, a slurry formed of water and a coloring or flavoring material might be used if desired.

The resulting puffed products when discharged from the nozzle and separated from the steam, should preferably be expanded in volume to a substantially smaller extent than products made in accordance with puffing techniques for forming ready-to-eat breakfast cereals. Generally, a maximum increase of about 4 times the original size of the particle is desired. Rice for example, when pufied in accordance with the principles of this invention, and when expanded to less than 4 times its original size, makes an excellent quick-cooking product which can readily be rehydrated by combining it with water and heating it to form a gelatinized cooked rice having excellent characteristics. Moreover, it has been found that for best results, the density of such puffed rice products should preferably lie within a range of about 350-650 grams per 120 cubic inches. This density range compares to a density of about 1,600 gm. per 120 cu. in. of polished rice before it is puffed.

The invention will be better understood with reference to the following examples:

diameter of 8 in., at a feed rate of about 40 lbs. per min. The following gun conditions were employed:

Steam pressure psig. Steam temperature 430F. Barrel angle below horizontal 4 Barrel rotation 78 rpm. Barrel temperature v 550%. Discharge nozzle orifice diameter 19/32 in.

'The rice kernels were discharged from the gun through the discharge nozzle into which water was introduced through an appropriate opening leading 'into the diverging portion of the nozzle (similar to that illustrated in FIG. 2), at a feed rate of about 0.7 lb. per min. The puffed kernels when discharged had a moisture content of about 7.5 percent, they had expanded to about 2% times their original size, they had a density of about 503 gm. per 12 cu. in., and the starch damage was determined 'to be about 100 percent.

A portion of the quick-cooking rice thus formed, was rehydrated to form a cooked rice product by combining 3 cups of rice with 1% cups of water. This mixture was brought to a vigorous boil and allowed to simmer for 6 min. The rice kernels absorbed all the water, they were completely cooked, they did not stick together, they retained their individual kernel shape, and they volume did not increase to any appreciable amount, as compared to the volume of the puffed kernels prior to cooking, and they had a density of about 1,600-1,700 gm. per cu. in.

EXAMPLE II Example I was repeated except that the water was pumped into the nozzle on the pressure. side of the constriction, at a feed rate of 0.95 lb. per min. The resulting quick-cooking rice when discharged had a moisture content of 7.9 percent, a bulk density of about 415 gm. per 120 cu. in., and a starch damage of about 97 percent. When rehydrated with water as described above, the rice likewise formed a cooked product having excellent qualities.

EXAMPLE nr Example I was repeated except that the water was introduced downstream from the nozzle at a distance of about 12 in. from the nozzle, at a feed rate of 0.75 lb. per min. The resulting puffed rice when discharged had a moisture content of about 8.5 percent, a density of 410 gm. per 120 cu. in., and a starch damage of about 99 percent. It likewise formed an excellent cooked rice when rehydrated with water as described in Example I.

EXAMPLE IV Example I was repeated except that liquified nitrogen was injected into the nozzle at a feed rate of about 2.0 lb. per min. The product density of the pufied rice was about 530 gm. per 120 cu. in., it was substantially completely gelatinized, and it fonned a good rice product when reconstituted with water.

EXAMPLE V Example I was repeated except that rice kernels were admitted into the gun at a feed rate of 30 lb. per min. and the puffed rice was enriched as it was discharged from the nozzle by pumping a slurry formed of 30 lb. of water, 7.5 gm. of Thiamine mononitrate, 2.8 gm. of Riboflavin, and 37.5 gm. of Niacin into the nozzle at a feed rate of 0.8 lb. per min. The resulting quick-cooking rice product had a bulk density of 520 gm. per 120 cu. in., a starch damage of 91 percent, and it contained a vitamin level of sufficient amounts to surpass the minimum standards of identity for enriched, precooked rice.

EXAMPLE VI One hundred pounds of white corn grits having a moisture content of about 5.5 percent and a density of 1,610 gm. per 120 cu. in., were preheated to a temperature of about 140 F., and then fed into a pufiing gun at a feed rate of 30 lb. per min. The following gun conditions were employed:

Steam pressure 100 psig. Steam temperature 415F. Barrel angle below horizontal 3 H2 Barrel rotation 90 rpm. Barrel temperature 700F. Discharge nozzle orifice diameter 21/32 in.

Water was introduced into the diverging portion of the discharge nozzle at a feed rate of 1.85 lb. per min. The puffed particles when discharged had a moisture content of 7.0 percent and a density of 785 gm. per 120 cu. in. It should be noted that the moisture content of the puffed particles was greater than the moisture content of the grits fed into the gun.

EXAMPLE VII Example VI was repeated except that no water was introduced into the nozzle. The resulting puffed particles had a moisture content of 5.0 percent, and a density of 580 gm. per 120 cu. in.

EXAMPLE VIII Ring-shaped pellets formed of a mixture including oat flour, water, and flavoring ingredients, and having a moisture content of about 13 percent and a density of about 1,400 gm. per 120 cu. in., were preheated to a temperature of about 160 F. and fed into a pufiing gun barrel at a feed rate of 10 lb. per min. The following gun conditions were employed:

Steam pressure 90 psig. Steam temperature 425F. Barrel angle 3 H2 Barrel rotation 70 rpm. Barrel temperature inlet end 790F. Barrel temperature outlet end 840F. Discharge nozzle orifice diameter 9/16 in.

Water was introduced into the discharge nozzle in the diverging portion thereof, at a feed rate of 2.3 lb. per min. The puffed particles when discharged were substantially completely gelatinized, they had expanded in volume to a lesser degree than when no water was injected into the nozzle, and they had a density of about 255 gm. per 120 cu. in.

EXAMPLE IX Fifty pounds of diced raw potato pieces of /2 inch cube, having a moisture content of about 30.5 percent, and a density of 760 gm. per 120 cu. in. were preheated to about 150 F. and fed into a puffing gun at a feed rate of about 13 lbs. per min. The following gun conditions were employed:

Steam pressure 45 psig. Steam temperature 460T. Barrel angle below horizontal 3 1/2" Barrel rotation 70 rpm. Barrel temperature 510F.

Discharge nozzle orifice diameter 18/32 in.

In the above description and attached drawing, a disclosure of the principles of this invention is presented, together with some of the specific examples by which the invention might be carried out.

Now, therefore, we claim:

1. In combination, an apparatus for expanding particles of a puffable material comprising a heated pressurized processing chamber having an inlet opening therein for introducing the particles into the chamber and a discharge orifice through which said particles are discharged, means associated with said chamber for causing the particles to move through the chamber, a nozzle member having a passage therethrough, means for attaching said nozzle to the discharge end of the chamber, and means including at least one passage for introducing a fluid medium into said nozzle whereby said fluid medium can be directed onto the surface of the particles as they are discharged through the nozzle.

2. The combination of claim 1 wherein said nozzle passage includes a portion which forms a discharge orifice having a prescribed size, and the fluid inlet passage is positioned in the nozzle so that the fluid medium is directed onto the particles after they are discharged through said orifice.

3. The combination of claim 1 wherein conduit means is attached to the nozzle and the fluid inlet passage. is positioned in said conduit means.

4. The combination of claim 1 wherein said nozzle passage includes a portion which forms a discharge orifice and the fluid inlet passage is positioned in the nozzle so that the fluid medium is directed onto the particles before they are discharged through said orifice.

5. The combination of claim 1 wherein means is provided for pumping the fluid medium through the fluid inlet passage.

6. The combination of claim 1 wherein a plurality of fluid inlet passages are provided for introducing the fluid medium into the nozzle.

7. The combination of claim 1 wherein the nozzle passage includes a cylindrical portion which forms the discharge orifice and a pair of frusto-conical portions which converge toward the cylindrical portion in such a manner that the cylindrical portion is interposed between the frusto-conical portions and all of said portions are aligned with respect to each other.

8. The combination of claim 1 wherein the pressurized processing chamber is a continuous puffing gun, said gun being adapted to cook particles of material and explosively puff them by subjecting the particles to moisture, temperature, and pressure conditions of sufficient magnitude to cause the particles to become at least partially gelatinized and expanded in volume when discharged from the gun.

9. A process for continuously processing and expanding particles of a putfable material which comprises introducing said particles into an inlet of a pressurized processing chamber having a nozzle with a discharge orifice therein, at least partially gelatinizing said particles by subjecting them to a heated pressurized processing fluid within the chamber, moving said particles from an inlet end of the chamber to a discharge end, discharging the particles and the medium through the nozzle and the discharge orifice into a reduced pressure environment thereby causing said particles to expand, and controlling the expansion and the bulk density of said particles by directing a fluid medium onto said particles as they are discharged through said nozzle.

10. The process of claim 9 whereby the expanded particles are increased in volume by a maximum amount of four times their original volume.

11. The process of claim 9 wherein the fluid medium is water and it is introduced into the nozzle at a feed rate of 025-50 pounds per minute.

12. The process of claim 9 wherein the fluid medium is liquid nitrogen.

13. The process of claim 9 wherein the fluid medium is comprised of a slurry which includes water and at least one other ingredient.

14. The process of claim ii wherein the particles of material are substantially gelatinized within the processing chamber.

15. The process of claim 9 wherein the particles are cooked and gelatinized in the gun barrel of a continuous puffing gun, and the pressurized processing fluid is steam. v

16. The process of claim 15 wherein the steam is introduced into the gun barrel at a pressure ranging from about 35-130 psig and at a temperature ranging from about 285-500 F., the particles are introduced into said barrel at a feed rate of -50 pounds per minute, and the fluid medium is introduced into the nozzle at a feed rate of about 0.255.0 pounds per minute.

17. The process of claim 9 which includes subjecting rice kernels to the heated pressurized processing fluid within the processing chamber, .said kernels becoming substantially gelatinized, the bulk density of the expanded kernels when discharged from said processing chamber ranging from about 350 to 650 grams per 120 cubic inches.

18. A process for making a quick-cooking rice product having a bulk density ranging from about 350-650 grams per cubic inches which comprises preheating kernels of rice to a prescribed temperature, introducing said kernels into the barrel of a continuous pufling gun at a prescribed feed rate, at least partially gelatinizing said kernels while in the gun barrel by treating them with steam having a pressure ranging from about 60-130 psig and a temperature ranging from about 

2. The combination of claim 1 wherein said nozzle passage includes a portion which forms a discharge orifice having a prescribed size, and the fluid inlet passage is positioned in the nozzle so that the fluid medium is directed onto the particles after they are discharged through said orifice.
 3. The combination of claim 1 wherein conduit means is attached to the nozzle and the fluid inlet passage is positioned in said conduit means.
 4. The combination of claim 1 wherein said nozzle passage includes a portion which forms a discharge orifice and the fluid inlet passage is positioned in the nozzle so that the fluid medium is directed onto the particles before they are discharged through said orifice.
 5. The combination of claim 1 wherein means is provided for pumping the fluid medium through the fluid inlet passage.
 6. The combination of claim 1 wherein a plurality of fluid inlet passages are provided for introducing the fluid medium into the nozzle.
 7. The combination of claim 1 wherein the nozzle passage includes a cylindrical portion which forms the discharge orifice and a pair of frusto-conical portions which converge toward the cylindrical portion in such a manner that the cylindrical portion is interposed between the frusto-conical portions and all of said portions are aligned with respect to each other.
 8. The combination of claim 1 wherein the pressurized processing chamber is a continuous puffing gun, said gun being adapted to cook particles of material and explosively puff them by subjecting the particles to moisture, temperature, and pressure conditions of sufficient magnitude to cause the particles to become at least partially gelatinized and expanded in volume when discharged from the gun.
 9. A process for continuously processing and expanding particles of a puffable material which comprises introducing said particles into an inlet of a pressurized processing chamber having a nozzle with a discharge orifice therein, at least partially gelatinizing said particles by subjecting them to a heated pressurized processing fluid within the chamber, moving said particles from an inlet end of the chamber to a discharge end, discharging the particles and the medium through the nozzle and the discharge orifice into a reduced pressure environment thereby causing said particles to expand, and controlling the expansion and the bulk density of said particles by directing a fluid medium onto said particles as they are discharged through said nozzle.
 10. The process of claim 9 whereby the expanded particles are increased in volume by a maximum amount of four times their original volume.
 11. The process of claim 9 wherein the fluid medium is water and it is introduced into the nozzle at a feed rate of 0.25-5.0 pounds per minute.
 12. The process of claim 9 wherein the fluid medium is liquid nitrogen.
 13. The process of claim 9 wherein the fluid medium is comprised of a slurry which includes water and at least one other ingredient.
 14. The process of claim 9 wherein the particles of material are substantially gelatinized within the processing chamber.
 15. The process of claim 9 wherein the particles are cooked and gelatinized in the gun barrel of a continuous puffing gun, and the pressurized processing fluid is steam.
 16. The process of claim 15 wherein the steam is introduced into the gun barrel at a pressure ranging from about 35-130 psig and at a temperature ranging from about 285*-500* F., the particles are introduced into said barrel at a feed rate of 5-50 pounds per minute, and the fluid medium is introduced into the nozzle at a feed rate of about 0.25-5.0 pounds per minute.
 17. The process of claim 9 which includes subjecting rice kernels to the heated pressurized processing fluid within the processing chamber, said kernels becoming substantially gelatinized, the bulk density of the expanded kernels when discharged from said processing chamber ranging from about 350 to 650 grams per 120 cubic inches.
 18. A process for making a quick-cooking rice product having a bulk density ranging from about 350-650 grams per 120 cubic inches which comprises preheating kernels of rice to a prescribed temperature, introducing said kernels into the barrel of a continuous puffing gun at a prescribed feed rate, at least partially gelatinizing said kernels while in the gun barrel by treating them with steam having a pressure ranging from about 60-130 psig and a temperature ranging from about 375*-500* F., moving said kernels from an inlet end of said barrel to a discharge end, discharging the cooked kernels through a discharge nozzle in the gun barrel into a reduced pressure environment thereby causing the kernels to explosively expand, and controlling the expansion of the kernels by introducing a fluid medium into the nozzle at a feed rate of about 0.4-3.0 pounds per minute and directing it onto the kernels as they are discharged through the dischArge nozzle and while they are expanding. 